Method and device for configuring signaling category for access control mechanism in wireless communication system

ABSTRACT

Provided are a method for a user equipment (UE) to perform early data transmission (EDT) in a wireless communication, and an apparatus supporting the same. The method may include: receiving system information including a threshold for the EDT; determining whether or not a condition for initiating the EDT is satisfied, by comparing the threshold for the EDT with a size of data for transmission; if the condition is satisfied, performing the EDT; and if the condition is not satisfied, performing a radio resource control (RRC) connection establishment or resume procedure.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the National Stage filing under 35 U.S.C. 371 ofInternational Application No. PCT/KR2018/008460, filed on Jul. 26, 2018,which claims the benefit of U.S. Provisional Application No. 62/537,456,filed on Jul. 27, 2017, and 62/537,457, filed on Jul. 27, 2017, thecontents of which are hereby incorporated by reference herein in theirentirety.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a wireless communication system, andmore particularly, to a method for a user equipment (UE) to performearly data transmission (EDT) and an apparatus supporting the same.

Related Art

In order to meet the demand for wireless data traffic, which has beenincreasing since the commercialization of a fourth-generation (4G)communication system, efforts are being made to develop an improvedfifth-generation (5G) communication system or pre-5G communicationsystem. For this reason, a 5G communication system or pre-5Gcommunication system is referred to as a beyond-4G-network communicationsystem or post-long-term evolution (LTE) system.

SUMMARY OF THE INVENTION

Meanwhile, for low cost UE, it is important to save UE power. Thus, thenumber of transmissions should be reduced as many as possible. Earlydata transmission (EDT) in RRC Connection Establishment or RRCConnection Resume is one of the solutions to reduce UE powerconsumption. However, the current system does not support early datatransmission. Thus, a method for a UE to perform EDT and an apparatussupporting the same need to be proposed.

One embodiment provides a method for performing, by a user equipment(UE), early data transmission (EDT) in a wireless communication. Themethod may include: receiving system information including a thresholdfor the EDT; determining whether or not a condition for initiating theEDT is satisfied, by comparing the threshold for the EDT with a size ofdata for transmission; if the condition is satisfied, performing theEDT; and if the condition is not satisfied, performing a radio resourcecontrol (RRC) connection establishment or resume procedure.

Another embodiment provides a user equipment (UE) performing early datatransmission (EDT) in a wireless communication. The UE may include: amemory; a transceiver; and a processor, connected to the memory and thetransceiver, that: controls the transceiver to receive systeminformation including a threshold for the EDT; determines whether or nota condition for initiating the EDT is satisfied, by comparing thethreshold for the EDT with a size of data for transmission; if thecondition is satisfied, performs the EDT; and if the condition is notsatisfied, performs a RRC connection establishment or resume procedure.

The power consumption of the UE can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows LTE system architecture.

FIG. 2 shows a control plane of a radio interface protocol of an LTEsystem.

FIG. 3 shows a user plane of a radio interface protocol of an LTEsystem.

FIG. 4 shows 5G system architecture.

FIG. 5 shows functional split between NG-RAN and 5GC.

FIG. 6 shows a contention based random access procedure.

FIG. 7 shows a non-contention based random access procedure.

FIG. 8 shows an example of MAC PDU including MAC header, MAC controlelements, MAC SDUs and padding.

FIG. 9 shows a procedure for determining whether or not to perform EDTaccording to an embodiment of the present invention.

FIGS. 10A and 10B show a procedure for performing EDT according to anembodiment of the present invention.

FIGS. 11A and 11B show a procedure for performing EDT according to anembodiment of the present invention.

FIG. 12 is a block diagram illustrating a method for a UE to perform EDTaccording to an embodiment of the present invention.

FIG. 13 is a block diagram illustrating a wireless communication systemaccording to the embodiment of the present invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

The technology described below can be used in various wirelesscommunication systems such as code division multiple access (CDMA),frequency division multiple access (FDMA), time division multiple access(TDMA), orthogonal frequency division multiple access (OFDMA), singlecarrier frequency division multiple access (SC-FDMA), etc. The CDMA canbe implemented with a radio technology such as universal terrestrialradio access (UTRA) or CDMA-2000. The TDMA can be implemented with aradio technology such as global system for mobile communications(GSM)/general packet ratio service (GPRS)/enhanced data rate for GSMevolution (EDGE). The OFDMA can be implemented with a radio technologysuch as institute of electrical and electronics engineers (IEEE) 802.11(Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, evolved UTRA (E-UTRA), etc.IEEE 802.16m is evolved from IEEE 802.16e, and provides backwardcompatibility with a system based on the IEEE 802.16e. The UTRA is apart of a universal mobile telecommunication system (UMTS). 3rdgeneration partnership project (3GPP) long term evolution (LTE) is apart of an evolved UMTS (E-UMTS) using the E-UTRA. The 3GPP LTE uses theOFDMA in a downlink and uses the SC-FDMA in an uplink. LTE-advanced(LTE-A) is an evolution of the LTE. 5G communication system is anevolution of the LTE-A.

For clarity, the following description will focus on LTE-A. However,technical features of the present invention are not limited thereto.

FIG. 1 shows LTE system architecture. The communication network iswidely deployed to provide a variety of communication services such asvoice over internet protocol (VoIP) through IMS and packet data.

Referring to FIG. 1, the LTE system architecture includes one or moreuser equipment (UE; 10), an evolved-UMTS terrestrial radio accessnetwork (E-UTRAN) and an evolved packet core (EPC). The UE 10 refers toa communication equipment carried by a user. The UE 10 may be fixed ormobile, and may be referred to as another terminology, such as a mobilestation (MS), a user terminal (UT), a subscriber station (SS), awireless device, etc.

The E-UTRAN includes one or more evolved node-B (eNB) 20, and aplurality of UEs may be located in one cell. The eNB 20 provides an endpoint of a control plane and a user plane to the UE 10. The eNB 20 isgenerally a fixed station that communicates with the UE 10 and may bereferred to as another terminology, such as a base station (BS), a basetransceiver system (BTS), an access point, etc. One eNB 20 may bedeployed per cell. There are one or more cells within the coverage ofthe eNB 20. A single cell is configured to have one of bandwidthsselected from 1.25, 2.5, 5, 10, and 20 MHz, etc., and provides downlinkor uplink transmission services to several UEs. In this case, differentcells can be configured to provide different bandwidths.

Hereinafter, a downlink (DL) denotes communication from the eNB 20 tothe UE 10, and an uplink (UL) denotes communication from the UE 10 tothe eNB 20. In the DL, a transmitter may be a part of the eNB 20, and areceiver may be a part of the UE 10. In the UL, the transmitter may be apart of the UE 10, and the receiver may be a part of the eNB 20.

The EPC includes a mobility management entity (MME) which is in chargeof control plane functions, and a system architecture evolution (SAE)gateway (S-GW) which is in charge of user plane functions. The MME/S-GW30 may be positioned at the end of the network and connected to anexternal network. The MME has UE access information or UE capabilityinformation, and such information may be primarily used in UE mobilitymanagement. The S-GW is a gateway of which an endpoint is an E-UTRAN.The MME/S-GW 30 provides an end point of a session and mobilitymanagement function for the UE 10. The EPC may further include a packetdata network (PDN) gateway (PDN-GW). The PDN-GW is a gateway of which anendpoint is a PDN.

The MME provides various functions including non-access stratum (NAS)signaling to eNBs 20, NAS signaling security, access stratum (AS)security control, Inter core network (CN) node signaling for mobilitybetween 3GPP access networks, idle mode UE reachability (includingcontrol and execution of paging retransmission), tracking area listmanagement (for UE in idle and active mode), P-GW and S-GW selection,MME selection for handovers with MME change, serving GPRS support node(SGSN) selection for handovers to 2G or 3G 3GPP access networks,roaming, authentication, bearer management functions including dedicatedbearer establishment, support for public warning system (PWS) (whichincludes earthquake and tsunami warning system (ETWS) and commercialmobile alert system (CMAS)) message transmission. The S-GW host providesassorted functions including per-user based packet filtering (by e.g.,deep packet inspection), lawful interception, UE Internet protocol (IP)address allocation, transport level packet marking in the DL, UL and DLservice level charging, gating and rate enforcement, DL rate enforcementbased on APN-AMBR. For clarity MME/S-GW 30 will be referred to hereinsimply as a “gateway,” but it is understood that this entity includesboth the MME and S-GW.

Interfaces for transmitting user traffic or control traffic may be used.The UE 10 and the eNB 20 are connected by means of a Uu interface. TheeNBs 20 are interconnected by means of an X2 interface. Neighboring eNBsmay have a meshed network structure that has the X2 interface. The eNBs20 are connected to the EPC by means of an S1 interface. The eNBs 20 areconnected to the MME by means of an S1-MME interface, and are connectedto the S-GW by means of S1-U interface. The S1 interface supports amany-to-many relation between the eNB 20 and the MME/S-GW.

The eNB 20 may perform functions of selection for gateway 30, routingtoward the gateway 30 during a radio resource control (RRC) activation,scheduling and transmitting of paging messages, scheduling andtransmitting of broadcast channel (BCH) information, dynamic allocationof resources to the UEs 10 in both UL and DL, configuration andprovisioning of eNB measurements, radio bearer control, radio admissioncontrol (RAC), and connection mobility control in LTE_ACTIVE state. Inthe EPC, and as noted above, gateway 30 may perform functions of pagingorigination, LTE_IDLE state management, ciphering of the user plane, SAEbearer control, and ciphering and integrity protection of NAS signaling.

FIG. 2 shows a control plane of a radio interface protocol of an LTEsystem. FIG. 3 shows a user plane of a radio interface protocol of anLTE system.

Layers of a radio interface protocol between the UE and the E-UTRAN maybe classified into a first layer (L1), a second layer (L2), and a thirdlayer (L3) based on the lower three layers of the open systeminterconnection (OSI) model that is well-known in the communicationsystem. The radio interface protocol between the UE and the E-UTRAN maybe horizontally divided into a physical layer, a data link layer, and anetwork layer, and may be vertically divided into a control plane(C-plane) which is a protocol stack for control signal transmission anda user plane (U-plane) which is a protocol stack for data informationtransmission. The layers of the radio interface protocol exist in pairsat the UE and the E-UTRAN, and are in charge of data transmission of theUu interface.

A physical (PHY) layer belongs to the L1. The PHY layer provides ahigher layer with an information transfer service through a physicalchannel. The PHY layer is connected to a medium access control (MAC)layer, which is a higher layer of the PHY layer, through a transportchannel A physical channel is mapped to the transport channel. Data istransferred between the MAC layer and the PHY layer through thetransport channel Between different PHY layers, i.e., a PHY layer of atransmitter and a PHY layer of a receiver, data is transferred throughthe physical channel using radio resources. The physical channel ismodulated using an orthogonal frequency division multiplexing (OFDM)scheme, and utilizes time and frequency as a radio resource.

The PHY layer uses several physical control channels. A physicaldownlink control channel (PDCCH) reports to a UE about resourceallocation of a paging channel (PCH) and a downlink shared channel(DL-SCH), and hybrid automatic repeat request (HARQ) information relatedto the DL-SCH. The PDCCH may carry a UL grant for reporting to the UEabout resource allocation of UL transmission. A physical control formatindicator channel (PCFICH) reports the number of OFDM symbols used forPDCCHs to the UE, and is transmitted in every subframe. A physicalhybrid ARQ indicator channel (PHICH) carries an HARQ acknowledgement(ACK)/non-acknowledgement (NACK) signal in response to UL transmission.A physical uplink control channel (PUCCH) carries UL control informationsuch as HARQ ACK/NACK for DL transmission, scheduling request, and CQI.A physical uplink shared channel (PUSCH) carries a UL-uplink sharedchannel (SCH).

A physical channel consists of a plurality of subframes in time domainand a plurality of subcarriers in frequency domain. One subframeconsists of a plurality of symbols in the time domain. One subframeconsists of a plurality of resource blocks (RBs). One RB consists of aplurality of symbols and a plurality of subcarriers. In addition, eachsubframe may use specific subcarriers of specific symbols of acorresponding subframe for a PDCCH. For example, a first symbol of thesubframe may be used for the PDCCH. The PDCCH carries dynamic allocatedresources, such as a physical resource block (PRB) and modulation andcoding scheme (MCS). A transmission time interval (TTI) which is a unittime for data transmission may be equal to a length of one subframe. Thelength of one subframe may be 1 ms.

The transport channel is classified into a common transport channel anda dedicated transport channel according to whether the channel is sharedor not. A DL transport channel for transmitting data from the network tothe UE includes a broadcast channel (BCH) for transmitting systeminformation, a paging channel (PCH) for transmitting a paging message, aDL-SCH for transmitting user traffic or control signals, etc. The DL-SCHsupports HARQ, dynamic link adaptation by varying the modulation, codingand transmit power, and both dynamic and semi-static resourceallocation. The DL-SCH also may enable broadcast in the entire cell andthe use of beamforming. The system information carries one or moresystem information blocks. All system information blocks may betransmitted with the same periodicity. Traffic or control signals of amultimedia broadcast/multicast service (MBMS) may be transmitted throughthe DL-SCH or a multicast channel (MCH).

A UL transport channel for transmitting data from the UE to the networkincludes a random access channel (RACH) for transmitting an initialcontrol message, a UL-SCH for transmitting user traffic or controlsignals, etc. The UL-SCH supports HARQ and dynamic link adaptation byvarying the transmit power and potentially modulation and coding. TheUL-SCH also may enable the use of beamforming. The RACH is normally usedfor initial access to a cell.

A MAC layer belongs to the L2. The MAC layer provides services to aradio link control (RLC) layer, which is a higher layer of the MAClayer, via a logical channel. The MAC layer provides a function ofmapping multiple logical channels to multiple transport channels. TheMAC layer also provides a function of logical channel multiplexing bymapping multiple logical channels to a single transport channel A MACsublayer provides data transfer services on logical channels.

The logical channels are classified into control channels fortransferring control plane information and traffic channels fortransferring user plane information, according to a type of transmittedinformation. That is, a set of logical channel types is defined fordifferent data transfer services offered by the MAC layer. The logicalchannels are located above the transport channel, and are mapped to thetransport channels.

The control channels are used for transfer of control plane informationonly. The control channels provided by the MAC layer include a broadcastcontrol channel (BCCH), a paging control channel (PCCH), a commoncontrol channel (CCCH), a multicast control channel (MCCH) and adedicated control channel (DCCH). The BCCH is a downlink channel forbroadcasting system control information. The PCCH is a downlink channelthat transfers paging information and is used when the network does notknow the location cell of a UE. The CCCH is used by UEs having no RRCconnection with the network. The MCCH is a point-to-multipoint downlinkchannel used for transmitting MBMS control information from the networkto a UE. The DCCH is a point-to-point bi-directional channel used by UEshaving an RRC connection that transmits dedicated control informationbetween a UE and the network.

Traffic channels are used for the transfer of user plane informationonly. The traffic channels provided by the MAC layer include a dedicatedtraffic channel (DTCH) and a multicast traffic channel (MTCH). The DTCHis a point-to-point channel, dedicated to one UE for the transfer ofuser information and can exist in both uplink and downlink. The MTCH isa point-to-multipoint downlink channel for transmitting traffic datafrom the network to the UE.

Uplink connections between logical channels and transport channelsinclude the DCCH that can be mapped to the UL-SCH, the DTCH that can bemapped to the UL-SCH and the CCCH that can be mapped to the UL-SCH.Downlink connections between logical channels and transport channelsinclude the BCCH that can be mapped to the BCH or DL-SCH, the PCCH thatcan be mapped to the PCH, the DCCH that can be mapped to the DL-SCH, andthe DTCH that can be mapped to the DL-SCH, the MCCH that can be mappedto the MCH, and the MTCH that can be mapped to the MCH.

An RLC layer belongs to the L2. The RLC layer provides a function ofadjusting a size of data, so as to be suitable for a lower layer totransmit the data, by concatenating and segmenting the data receivedfrom an upper layer in a radio section. In addition, to ensure a varietyof quality of service (QoS) required by a radio bearer (RB), the RLClayer provides three operation modes, i.e., a transparent mode (TM), anunacknowledged mode (UM), and an acknowledged mode (AM). The AM RLCprovides a retransmission function through an automatic repeat request(ARQ) for reliable data transmission. Meanwhile, a function of the RLClayer may be implemented with a functional block inside the MAC layer.In this case, the RLC layer may not exist.

A packet data convergence protocol (PDCP) layer belongs to the L2. ThePDCP layer provides a function of header compression function thatreduces unnecessary control information such that data being transmittedby employing IP packets, such as IPv4 or IPv6, can be efficientlytransmitted over a radio interface that has a relatively smallbandwidth. The header compression increases transmission efficiency inthe radio section by transmitting only necessary information in a headerof the data. In addition, the PDCP layer provides a function ofsecurity. The function of security includes ciphering which preventsinspection of third parties, and integrity protection which preventsdata manipulation of third parties.

A radio resource control (RRC) layer belongs to the L3. The RLC layer islocated at the lowest portion of the L3, and is only defined in thecontrol plane. The RRC layer takes a role of controlling a radioresource between the UE and the network. For this, the UE and thenetwork exchange an RRC message through the RRC layer. The RRC layercontrols logical channels, transport channels, and physical channels inrelation to the configuration, reconfiguration, and release of RBs. AnRB is a logical path provided by the L1 and L2 for data delivery betweenthe UE and the network. That is, the RB signifies a service provided theL2 for data transmission between the UE and E-UTRAN. The configurationof the RB implies a process for specifying a radio protocol layer andchannel properties to provide a particular service and for determiningrespective detailed parameters and operations. The RB is classified intotwo types, i.e., a signaling RB (SRB) and a data RB (DRB). The SRB isused as a path for transmitting an RRC message in the control plane. TheDRB is used as a path for transmitting user data in the user plane.

Referring to FIG. 2, the RLC and MAC layers (terminated in the eNB onthe network side) may perform functions such as scheduling, automaticrepeat request (ARQ), and hybrid automatic repeat request (HARQ). TheRRC layer (terminated in the eNB on the network side) may performfunctions such as broadcasting, paging, RRC connection management, RBcontrol, mobility functions, and UE measurement reporting andcontrolling. The NAS control protocol (terminated in the MME of gatewayon the network side) may perform functions such as a SAE bearermanagement, authentication, LTE_IDLE mobility handling, pagingorigination in LTE_IDLE, and security control for the signaling betweenthe gateway and UE.

Referring to FIG. 3, the RLC and MAC layers (terminated in the eNB onthe network side) may perform the same functions for the control plane.The PDCP layer (terminated in the eNB on the network side) may performthe user plane functions such as header compression, integrityprotection, and ciphering.

FIG. 4 shows 5G system architecture.

Referring to FIG. 4, a Next Generation Radio Access Network (NG-RAN)node may be either a gNB providing NR Radio Access (NR) user plane andcontrol plane protocol terminations towards the UE or an ng-eNBproviding Evolved Universal Terrestrial Radio Access (E-UTRA) user planeand control plane protocol terminations towards the UE. The gNBs andng-eNBs may be interconnected with each other by means of the Xninterface. The gNBs and ng-eNBs may be also connected by means of the NGinterfaces to the 5G Core Network (5GC), more specifically to the AMF(Access and Mobility Management Function) by means of the NG-C interfaceand to the UPF (User Plane Function) by means of the NG-U interface. TheNG-C may be control plane interface between NG-RAN and 5GC, and the NG-Umay be user plane interface between NG-RAN and 5GC.

FIG. 5 shows functional split between NG-RAN and 5GC.

Referring to FIG. 5, the gNB and ng-eNB may host the followingfunctions:

-   -   Functions for Radio Resource Management: Radio Bearer Control,        Radio Admission Control, Connection Mobility Control, Dynamic        allocation of resources to UEs in both uplink and downlink        (scheduling);    -   IP header compression, encryption and integrity protection of        data;    -   Selection of an AMF at UE attachment when no routing to an AMF        can be determined from the information provided by the UE;    -   Routing of User Plane data towards UPF(s);    -   Routing of Control Plane information towards AMF;    -   Connection setup and release;    -   Scheduling and transmission of paging messages;    -   Scheduling and transmission of system broadcast information        (originated from the AMF or O&M);    -   Measurement and measurement reporting configuration for mobility        and scheduling;    -   Transport level packet marking in the uplink;    -   Session Management;    -   Support of Network Slicing;    -   QoS Flow management and mapping to data radio bearers;    -   Support of UEs in RRC_INACTIVE state;    -   Distribution function for NAS messages;    -   Radio access network sharing;    -   Dual Connectivity;    -   Tight interworking between NR and E-UTRA.

The Access and Mobility Management Function (AMF) may host the followingmain functions:

-   -   NAS signalling termination;    -   NAS signalling security;    -   AS Security control;    -   Inter CN node signalling for mobility between 3GPP access        networks;    -   Idle mode UE Reachability (including control and execution of        paging retransmission);    -   Registration Area management;    -   Support of intra-system and inter-system mobility;    -   Access Authentication;    -   Access Authorization including check of roaming rights;    -   Mobility management control (subscription and policies);    -   Support of Network Slicing;    -   SMF selection.

The User Plane Function (UPF) may host the following main functions:

-   -   Anchor point for Intra-/Inter-RAT mobility (when applicable);    -   External PDU session point of interconnect to Data Network;    -   Packet routing & forwarding;    -   Packet inspection and User plane part of Policy rule        enforcement;    -   Traffic usage reporting;    -   Uplink classifier to support routing traffic flows to a data        network;    -   Branching point to support multi-homed PDU session;    -   QoS handling for user plane, e.g. packet filtering, gating,        UL/DL rate enforcement;    -   Uplink Traffic verification (SDF to QoS flow mapping);    -   Downlink packet buffering and downlink data notification        triggering.

The Session Management function (SMF) may host the following mainfunctions:

-   -   Session Management;    -   UE IP address allocation and management;    -   Selection and control of UP function;    -   Configures traffic steering at UPF to route traffic to proper        destination;    -   Control part of policy enforcement and QoS;    -   Downlink Data Notification.

Hereinafter, a random access procedure in LTE system is described.

First of all, a user equipment performs a random access procedure in theevent of one of the following cases.

-   -   Case that a user equipment performs an initial access without a        connection (e.g., RRC connection) to a base station    -   Case that a user equipment initially accesses a target cell by a        handover procedure    -   Case requested by a command given by a base station    -   Case that data in uplink is generated in a situation that an        uplink time synchronization is not matched or a radio resource        used to request a radio resource is not allocated    -   Case of a recovery process in case of a radio link failure (RLF)        or a handover failure

In LTE system, a non-contention based random access procedure isprovided as follows. First of all, a base station assigns a dedicatedrandom access preamble designated to a specific user equipment.Secondly, the corresponding user equipment performs a random accessprocedure using the random access preamble. So to speak, in a processfor selecting a random access preamble, there are a contention basedrandom access procedure and a non-contention based random accessprocedure. In particular, according to the contention based randomaccess procedure, a user equipment randomly selects one random accesspreamble from a specific set and then uses the selected random accesspreamble. According to the non-contention based random access procedure,a random access preamble assigned by a base station to a specific userequipment only is used. Differences between the two kinds of the randomaccess procedures lie in a presence or non-presence of occurrence of acontention problem. The non-contention based random access procedure canbe used, as mentioned in the foregoing description, only if a handoverprocess is performed or it is requested by a command given by a basestation.

FIG. 6 shows a contention based random access procedure.

In step S610, in a contention based random access procedure, a userequipment randomly selects a random access preamble from a set of randomaccess preambles indicated through a system information or a handovercommand, selects a PRACH (physical RACH) resource capable of carryingthe selected random access preamble, and then transmits thecorresponding random access preamble through the selected resource.

In step S620, after the user equipment has transmitted the random accesspreamble in the above manner, it attempts a reception of its randomaccess response within a random access response receiving windowindicated through the system information or the handover command from abase station. In particular, the random access response information istransmitted in format of MAC PDU. And, the MAC PDU is delivered throughPDSCH (physical downlink shared channel). In order for the userequipment to appropriately receive the information delivered through thePDSCH, PDCCH is delivered as well. In particular, information on theuser equipment supposed to receive the PDSCH, frequency and timeinformation of a radio resource of the PDSCH, a transmission format ofthe PDSCH and the like are included in the PDCCH. Once the userequipment successfully receives the PDCCH transmitted to itself, theuser equipment appropriately receives a random access responsetransmitted on the PDSCH according to the informations of the PDCCH.And, in the random access response, a random access preamble identifier(ID), a UL grant (UL radio resource), a temporary cell identifier(temporary C-RNTI) and time alignment commands (time synchronizationcorrection values, hereinafter abbreviated TAC) are included. Asmentioned in the above description, the random access preambleidentifier is required for the random access response. The reason forthis is described as follows. First of all, since random access responseinformation for at least one or more user equipments may be included ina single random access response, it is necessary to notify that the ULgrant, the temporary C-RNTI and the TAC are valid for which one of theuser equipments. And, the random access preamble identifier matches therandom access preamble selected by the user equipment in the step S610.

In step S630, if the user equipment receives the random access responsevalid for itself, the user equipment individually processes each of theinformation included in the received random access response. Inparticular, the user equipment applies the TAC and saves the temporaryC-RNTI. Moreover, the user equipment transmits a data saved in itsbuffer or a newly generated data to the base station using the receivedUL grant. In this case, the data included in the UL grant should containan identifier of the user equipment. In the contention based randomaccess procedure, the base station is unable to determine what kinds ofuser equipments perform the random access procedure. Hence, in order toresolve the contention in the future, the base station should identifythe corresponding user equipment. The identifier of the user equipmentcan be included by one of two kinds of methods as follows. First of all,if the user equipment has a valid cell identifier previously assigned bya corresponding cell prior to the random access procedure, the userequipment transmits its cell identifier through the UL grant. On thecontrary, if the user equipment fails in receiving the valid cellidentifier prior to the random access procedure, the user equipmenttransmits its unique identifier (e.g., S-TMSI, Random Id, etc.)inclusively. In general, the unique ID is longer than a cell identifier.If the user equipment transmits the data through the UL grant, the userequipment initiates a timer for contention resolution (hereinaftercalled a contention resolution timer).

In step S640, after the user equipment has transmitted the datacontaining its identifier through the UL grant included in the randomaccess response, it waits for an indication from the base station forthe contention resolution. In particular, the user equipment attempts areception of the PDCCH in order to receive a specific message. Inreceiving the PDCCH, there are two kinds of methods. As mentioned in theforegoing description, if the user equipment's identifier transmittedthrough the UL grant is the cell identifier, the user equipment attemptsa reception of the PDCCH using its cell identifier. If the identifier isthe unique identifier, the user equipment attempts the reception of thePDCCH using the temporary C-RNTI included in the random access response.Thereafter, in the former case, if the user equipment receives the PDCCHthrough its cell identifier before the expiration of the contentionresolution timer, the user equipment determines that the random accessprocedure has been normally performed and then ends the random accessprocedure. In the latter case, if the user equipment receives the PDCCHthrough the temporary cell identifier before the expiration of thecontention resolution timer, the user equipment checks data delivered bythe PDSCH indicated by the PDCCH. If the unique identifier of the userequipment is included in the substance of the data, the user equipmentdetermines that the random access procedure has been normally performedand then ends the random access procedure.

FIG. 7 shows a non-contention based random access procedure.

Unlike the contention based random access procedure, in a non-contentionbased random access procedure, if a random access response informationis received, a random access procedure is ended by determining that therandom access procedure has been normally performed. The non-contentionbased random access procedure may exist in one of the two cases, i.e., afirst case of a handover process and a second case requested by acommand given by a base station. Of course, a contention based randomaccess procedure can be performed in one of the two cases. First of all,for a non-contention based random access procedure, it is important toreceive a designated random access preamble having no possibility incontention from a base station. The random access preamble can beindicated by a handover command or a PDCCH command After the basestation has assigned the random access preamble designated only to theuser equipment, the user equipment transmits the preamble to the basestation.

Hereinafter, a protocol data unit (PDU) is described.

A MAC PDU is a bit string that is byte aligned (i.e. multiple of 8 bits)in length. MAC SDUs are bit strings that are byte aligned (i.e. multipleof 8 bits) in length. A service data unit (SDU) is included into a MACPDU from the first bit onward.

FIG. 8 shows an example of MAC PDU including MAC header, MAC controlelements, MAC SDUs and padding.

Referring to FIG. 8, a MAC PDU consists of a MAC header, zero or moreMAC SDUs, zero or more MAC control elements, and optionally padding.Both the MAC header and the MAC SDUs are of variable sizes. Both the MACheader and the MAC SDUs are of variable sizes. A MAC PDU header consistsof one or more MAC PDU subheaders. Each subheader corresponds to eithera MAC SDU, a MAC control element or padding. A MAC PDU subheaderconsists of the five or six header fields R/F2/E/LCID/(F)/L but for thelast subheader in the MAC PDU and for fixed sized MAC control elements.The last subheader in the MAC PDU and subheaders for fixed sized MACcontrol elements consist solely of the four header fields R/F2/E/LCID. AMAC PDU subheader corresponding to padding consists of the four headerfields R/F2/E/LCID.

MAC PDU subheaders have the same order as the corresponding MAC SDUs,MAC control elements and padding. MAC control elements are always placedbefore any MAC SDU. Padding occurs at the end of the MAC PDU, exceptwhen single-byte or two-byte padding is required. Padding may have anyvalue and the MAC entity shall ignore it. When padding is performed atthe end of the MAC PDU, zero or more padding bytes are allowed. Whensingle-byte or two-byte padding is required, one or two MAC PDUsubheaders corresponding to padding are placed at the beginning of theMAC PDU before any other MAC PDU subheader. A maximum of one MAC PDU canbe transmitted per transport block (TB) per MAC entity. A maximum of oneMCH MAC PDU can be transmitted per transmission time interval (TTI).

Meanwhile, for low cost UE, it is important to save UE power. Forexample, the low cost UE includes Narrow Band Internet of Things(NB-IoT) UE, Bandwidth reduced Low complexity (BL) UE, Machine TypeCommunication (MTC) UE or a UE in enhanced coverage. Thus, the number oftransmissions should be reduced as many as possible. Early datatransmission (EDT) in RRC Connection Establishment or RRC ConnectionResume is one of the solutions to reduce UE power consumption. However,the current system does not support early data transmission.Hereinafter, a method for a UE to perform EDT and an apparatussupporting the same according to an embodiment of the present inventionare described in detail. In the specification, the EDT may be uplinkdata transmission during the random access procedure. The EDT may allowone uplink data transmission optionally followed by one downlink datatransmission during the random access procedure. For example, the EDTmay allow one uplink data transmission optionally followed by onedownlink data transmission during the random access procedure withoutestablishing or resuming the RRC connection. S1 connection may beestablished or resumed upon reception of the uplink data and may bereleased or suspended after transmission of the downlink data. Earlydata transmission may refer to both control plane (CP)-EDT and userplane (UP)-EDT.

According to an embodiment of the present invention, while performingstate transition procedure such as RRC connection establishmentprocedure or RRC connection resume procedure, the UE may transmit datain a message over signaling radio bearer (SRB) such as DCCH or CCCH. Themessage may be a NAS message or a RRC message such as RRC ConnectionRequest message or RRC connection resume message. Alternatively, whileperforming state transition procedure such as RRC connectionestablishment procedure or RRC connection resume procedure, the UE maytransmit data in a message over data radio bearer (DRB) configured forEDT.

FIG. 9 shows a procedure for determining whether or not to perform EDTaccording to an embodiment of the present invention.

The EDT may be triggered when the upper layers have requested theestablishment or resumption of the RRC Connection for Mobile Originateddata (i.e., not signaling or SMS) and the uplink data size is less thanor equal to a transport block (TB) size indicated in the systeminformation. The EDT may be not used for data over the control planewhen using the User Plane CIoT EPS optimizations. The EDT may beapplicable to BL UEs, UEs in enhanced coverage or NB-IoT UEs. The EDTmay be initiated by the upper layers (e.g. UE RRC).

Referring to FIG. 9, in step S910, the UE may receive system informationincluding a threshold for the EDT, from a base station. The thresholdfor the EDT may be a threshold related to a size of data for EDT. Thethreshold for the EDT may be a threshold related to QoS characteristics,maximum bit rate or delay requirement to the UE. For example, the systeminformation may be defined as table 1.

TABLE 1 EDT-TBS-NB-r15 ::= SEQUENCE { edt-SmallTBS-Enabled-r15 BOOLEAN,edt-TBS-r15 ENUMERATED {b328, b408, b504, b584, b680, b808, b936, b1000}}

Referring to table 1, the edt-SmallTBS-Enabled may be a value TRUE whichindicates that UE performing EDT is allowed to select TBS smaller thanedt-TBS for Msg3 according to the corresponding NPRACH resource. Theedt-TBS may be largest TBS for Msg3 for a NPRACH resource applicable toa UE performing EDT. Value in bits. Value b328 corresponds to 328 bits,value b408 corresponds to 408 bits and so on. The edt-TBS may be athreshold related to a size of data for EDT

In step S920, the UE may determine whether or not a condition forinitiating EDT is satisfied, based on the threshold and a size of datafor transmission. The data for transmission may be a layer 2 data orlayer 3 data. For example, the layer 2 data may be MAC PDU. For example,the size of data may be uplink data available for transmission plus MACheader and, where required, MAC control elements.

Specifically, the UE may compare the threshold for EDT with the size ofdata for transmission. Then, the UE may determine whether or not thecondition for initiating EDT is satisfied, by comparing the thresholdfor EDT with the size of data for transmission.

-   -   Option 1: If the size of data for transmission is lower than the        threshold for EDT, the UE may determine that the condition for        initiating EDT is satisfied. In this case, in step S930, the UE        may perform the EDT. Namely, the UE may transmit data to the        base station by using message 3 during the random access        procedure.    -   Option 2: If the size of data for transmission is higher than        the threshold for EDT, the UE may determine that the condition        for initiating EDT is not satisfied. In this case, in step S935,        the UE may not perform the EDT. Namely, the UE may transmit data        to the base station after completion of RRC connection        establishment or resume procedure. For example, in case that the        size of data for transmission is higher than the threshold for        EDT, the UE may transmit data to the base station after the UE        transits from RRC_IDLE to RRC_CONNECTED. Further, a UE MAC may        indicates to UE RRC that EDT is cancelled.

Furthermore, the UE may determine whether or not a condition forinitiating EDT is satisfied, based on the threshold and delayrequirement of the data. The threshold may be a threshold related todelay requirement for EDT. The UE may determine whether or not the datafor transmission satisfies the delay requirement for EDT. If the delayrequirement of the data is lower than the threshold for EDT, the UE maydetermine that the data for transmission satisfies the delay requirementfor EDT. If the delay requirement of the data is higher than thethreshold for EDT, the UE may determine that the data for transmissiondoes not satisfy the delay requirement for EDT.

According to an embodiment of the present invention, the UE candetermine whether or not to perform EDT during the random accessprocedure. For example, in case that the size of data for transmissionis lower than the threshold for EDT, the UE may transmit data to thebase station by using message 3 during the random access procedure.Thus, the power consumption of the UE (e.g. low cost UE) can be reduced.

According to an embodiment of the present invention, configuration ofradio bearers may be mapped to EDT. If a cell indicates EDT for the UserPlane CIoT EPS optimization, the UE supporting EDT for User Plane CIoTEPS optimization may configure DRB(s) (including RLC/PDCP entities andlogical channels) mapped to EDT. The UE in RRC_CONNECTED may beconfigured with the DRB(s) mapped to EDT and other DRB(s) not mapped toEDT. If the UE receives RRC connection release indicating suspendindication and the DRB(s) mapped to EDT, and if the cell indicates EDTfor the User Plane CIoT EPS optimization, the UE establishing a RRCconnection at the cell may be allowed to transmit data available fortransmission over the DRB(s) mapped to EDT while in the RRC connectionestablishment or resume procedure. However, the UE may be not allowed totransmit data available for transmission over the DRB(s) not mapped toEDT in the RRC connection establishment or resume procedure. If the UEtransmits a MAC PDU including data over the DRB(s) mapped to EDT, a LCIDindicating the DCCH mapped to EDT may be included as a MAC sub-header ofthe MAC PDU. The embodiment of the present invention may be appliedtogether with the example in FIGS. 10A and 10B.

According to an embodiment of the present invention, EDT may be allowedper priority. For controlling EDT, the base station may indicate one ormore priorities to the UE via system information or a dedicated RRCmessage such as RRC connection release message. The priority may be oneof a logical channel priority and a Per Packet Priority. The prioritymay be mapped to one or more radio bearers or logical channels mapped toEDTs. The base station may inform the UE which priorities are allowed toperform EDT during the RRC connection establishment or resume procedure.Thus, if data becomes available for a radio bearer or a logical channel,and if the base station indicates that the priority of the radio beareror the logical channel is allowed for EDT, the UE may perform EDT.Otherwise, the UE may not perform EDT. That is, the UE may perform datatransmission after completion of RRC connection establishment or resumeprocedure. The embodiment of the present invention may be appliedtogether with the example in FIGS. 10A and 10B.

According to an embodiment of the present invention, for controllingEDT, the base station may indicate one or more QoS class identifiers(QCIs) to the UE via system information or a dedicated RRC message suchas RRC connection release message. The QCI may be mapped to one or moreradio bearers or logical channels mapped to EDTs. The base station mayinform the UE which QCI(s) are allowed to perform EDT during RRCconnection establishment or resume procedure. Thus, if data becomesavailable for a radio bearer or a logical channel, and if the basestation indicates that the QCI of the radio bearer or the logicalchannel is allowed for EDT, the UE may perform EDT. Otherwise, the UEmay not perform EDT. That is, the UE may perform data transmission aftercompletion of RRC connection establishment or resume procedure. Theembodiment of the present invention may be applied together with theexample in FIGS. 10A and 10B.

According to an embodiment of the present invention, for controllingEDT, the base station may indicate one or more QoS flows to the UE viasystem information or a dedicated RRC message such as RRC connectionrelease message. The QoS flow may be mapped to one or more radio bearersor logical channels mapped to EDTs. The base station may inform the UEwhich QoS flow(s) are allowed to perform EDT during RRC connectionestablishment or resume procedure. Thus, if data becomes available for aradio bearer or a logical channel, and if the base station indicatesthat the QoS flow of the radio bearer or the logical channel is allowedfor EDT, the UE may perform EDT. Otherwise, the UE may not perform EDT.That is, the UE may perform data transmission after completion of RRCconnection establishment or resume procedure. The embodiment of thepresent invention may be applied together with the example in FIGS. 10Aand 10B.

According to an embodiment of the present invention, EDT may be allowedbased on QoS characteristics such as bit rate or delay. For controllingEDT, the base station may indicate one or more thresholds. The one ormore thresholds may be related to at least one of QoS characteristics,the amount of data (e.g. a size of data), (maximum) bit rate or delayrequirement to the UE via system information or a dedicated RRC messagesuch as RRC connection release message. The QoS characteristics,(maximum) bit rate or delay requirement may be mapped to one or moreradio bearers or logical channels mapped to EDTs.

For example, the base station may inform the UE about maximum bit ratewhich is allowed to perform EDT during RRC connection establishment orresume procedure. Thus, if data becomes available for a radio bearer ora logical channel, and if the amount of data (e.g. a size of data orsize of message) available for transmission is lower than the thresholdindicated by the base station, UE performs EDT. The threshold may beincluded in the system information, and the data may be in layer 2 (e.g.MAC PDU) and/or layer 3 (e.g. RRC message). Otherwise, the UE may notperform EDT. That is, the UE may perform data transmission aftercompletion of RRC connection establishment or resume procedure.

For example, the base station may inform the UE about delay requirementwhich is allowed to perform EDT during RRC connection establishment orresume procedure. Thus, if data becomes available for a radio bearer ora logical channel, and if the amount of data (e.g. a size of data orsize of message) available for transmission should meet the delayrequirement indicated by the base station, e.g. the data should betransmitted within 100 ms indicated by the base station, the UE mayperform EDT. Otherwise, the UE may not perform EDT. That is, the UE mayperform data transmission after completion of RRC connectionestablishment or resume procedure. The embodiment of the presentinvention may be applied together with the example in FIGS. 10A and 10B.

FIGS. 10A and 10B show a procedure for performing EDT according to anembodiment of the present invention.

Referring to FIGS. 10A and 10B, in step S1000, the UE may camp on acell. For example, the cell may be a NB-IoT cell or a LTE cellsupporting one or more narrowband for low cost UE capabilities suchCategory M1.

In step S1010, the UE may receive system information from a base stationvia the cell. The system information may broadcast at least one ofconfiguration of CCCH2 for EDT, configuration of radio bearers (e.g.DRBs including DTCHs) mapped to EDT, RAPID indicating EDT or LCID ofCCCH2 for EDT. Each cell may inform one or more UEs that this cellsupports EDT for the Control Plane CIoT EPS optimization and/or EDT forthe User Plane CIoT EPS optimization via system information.

If the cell indicates EDT for the User Plane CIoT EPS optimization, theUE supporting EDT for User Plane CIoT EPS optimization may configureDRB(s) (including RLC/PDCP entities and logical channels) mapped to EDT.In this case, the UE may configure one CCCH logical channel and one ormore DTCH logical channels for uplink. The CCCH logical channel may havea higher priority than the DTCH logical channel(s) mapped to EDT and allMAC Control Elements. The DTCH logical channel(s) mapped to EDT may havea higher priority than some or all of MAC Control Element(s) (e.g. TheData Volume and Power Headroom Report (DPR) MAC control element, BufferStatus Report MAC Control Element, Power Headroom MAC Control Element).The DTCH logical channel(s) mapped to EDT may have a higher prioritythan the DTCH logical channels not mapped to EDT.

If the cell indicates EDT for the Control Plane CIoT EPS optimization,the UE supporting EDT for Control Plane CIoT EPS optimization mayconfigure CCCH2 for EDT. In this case, the UE may configure twodifferent CCCH logical channels for uplink. The first CCCH logicalchannel may have a higher priority than the second CCCH logical channelin MAC logical channel prioritization. The first CCCH logical channelmay be SRB0 while the second CCCH logical channel may be SRB0bis. Thefirst CCCH logical channel may be applicable for uplink and downlink,while the second CCCH logical channel may be applicable only for uplink.The first CCCH logical channel may have a higher priority than all MACControl Elements. The second CCCH logical channel may have a lowerpriority than a certain MAC Control Element(s) (e.g. The Data Volume andPower Headroom Report (DPR) MAC control element, Buffer Status ReportMAC Control Element, Power Headroom MAC Control Element). The secondCCCH logical channel may have a higher priority than the other MACControl Element(s). Alternatively, both CCCH logical channels may have ahigher priority than all MAC Control Elements.

The CCCH2 may be replaced by DCCH mapped to EDT or a legacy CCCH. Forexample, DCCH mapped to EDT may be used to carry EDT instead of CCCH2.However, DCCH not mapped to EDT may not be used to carry EDT.

If the cell does not indicate EDT, UE does not perform EDT.

In step S1020, if the UE has been suspended after release of theprevious RRC connection, DTCH(s) mapped to EDT may have been configuredbut suspended for the UE. In this case, if UE detects UL data for theDTCH(s), the UE may resume the DTCH(s) mapped to EDT and then submit theUL data to lower layers (RLC/PDCP entities) over the DTCH mapped to EDT.This behavior may not be applied to DTCHs (i.e. DRBs) not mapped to EDT.Thus, the UE may not perform EDT for UL data over DTCHs (i.e. DRBs) notmapped to EDT. If the UE detects UL data, the UE may also trigger RRCconnection establishment procedure or RRC connection resume procedure.The RRC connection request message or the RRC connection resume requestmessage may be submitted to CCCH1 for SRB0.

In step S1030, if a random access procedure is triggered, the MAC layerof the UE (i.e. UE MAC) may select one of random access preambleidentifiers (RAPIDs) mapped to EDT (as received from the cell via systeminformation). Then, the UE may transmit a random access preamble withthe selected random access preamble identifier (RAPID).

In step S1040, the UE MAC may receive a random access response (RAR)message indicating the transmitted RAPID and an uplink grant. If the UEMAC receives no RAR indicating the transmitted RAPID, the UE MACre-transmits a random access preamble with power ramping.

The UE MAC may perform logical channel prioritization. Then, the UE MACmay construct MAC PDU based on logical channel priorities and the uplinkgrant. In the logical channel prioritization, CCCH1 and the DCCHs mappedto EDT may have a higher priority than all MAC Control Elements and theother DCCHs not mapped to EDT.

In the MAC PDU, if data from CCCH is included, LCID indicating CCCH maybe included as a MAC sub-header. In addition, if data from the DCCHmapped to EDT is included, LCID indicating the DCCH mapped to EDT may beincluded as a MAC sub-header.

If the received UL grant can accommodate all UL data in the DCCH mappedto EDT, and if the UE has no remaining UL data over any logical channel,the UE may include buffer status reporting (BSR) MAC Control Elementindicating no data, Data Volume and Power Headroom Report (DPR) MACControl Element indicating no data (i.e. DV value=0), or no MAC ControlElement.

If the received UL grant can accommodate some UL data in the DCCH mappedto EDT with a MAC Control Element such as BSR MAC CE or DPR MAC CE, andif the UE has remaining UL data over any logical channel, the UE mayinclude BSR MAC CE indicating the amount of the remaining UL data or DPRMAC CE indicating the amount of the remaining UL data.

If the received UL grant cannot accommodate any UL data in the DCCHmapped to EDT with a MAC Control Element such as BSR MAC CE or DPR MACCE, the UE may include BSR MAC CE indicating the amount of the remainingUL data or DPR MAC CE indicating the amount of the remaining UL data.

In step S1050, the UE MAC may transmit the MAC PDU (i.e. Message 3(MSG3)) to the base station by using the uplink grant.

In step S1060, if the UE MAC may receive contention resolution to themessage 3 from the base station (e.g. via PDCCH or Contention ResolutionMAC CE), the UE MAC may consider the RACH procedure successful.Otherwise, the UE MAC may re-transmit a random access preamble.

The UE may receive RRC connection setup message or RRC connection resumemessage from the base station. If the received message indicates NACK toEDT, the layer of the UE received the NACK may send the NACK to a higherlayer of the UE. For example, for EDT over SRB in Control Plane CIoT EPSoptimization, if the UE RRC receives the NACK from the message, the UERRC may inform UE NAS about the NACK to the UL data. Upon receiving theNACK, the higher layer of the UE (e.g. UE NAS) may re-transmit the ULdata. If so, the UE RRC may create a RRC message including the UL dataand submit the RRC message to lower layers (e.g. PDCP/RLC/MAC). The RRCmessage may be carried over either CCCH2 or DCCH. If the message iscarried over DCCH, the message may be a RRC connection setup/resumecomplete including UL data. The UL data may include UL data which isNACKed and/or remaining UL data. Thus, the UE may transmit a single MACSDU including RRC connection setup/resume complete including UL datawith a MAC CE in a single MAC PDU. The MAC CE in the MAC PDU may beeither BSR MAC CE indicating the amount of the remaining UL data or DPRMAC CE indicating the amount of the remaining UL data. If there is noremaining UL data except the UL data included in the MAC PDU, the MAC CEmay indicate no data.

If the UE receives a RRC message indicating that the data areacknowledged, the UE may consider that the data are acknowledged inLayer 1, 2 or 3, and the UE may stop (re-)transmissions of any data andRLC/MAC acknowledgements, if any. The UE may release the RRC connectionand Layer 2 entities, and enter RRC_IDLE. The RRC message may be one ofRRC connection release, a RRC connection reject message, a RRCconnection setup message and a RRC connection resume message.

For example, if the MAC CE indicates no data, and if the base stationsuccessfully receives all UL data, in case there is no DL data, the basestation may transmit RRC connection release indicating ACK to the ULdata. Upon receiving the RRC connection release indicating ACK to the ULdata, the UE may consider that the UL data that were transmitted areacknowledged and enter RRC_IDLE. The UE RRC may inform UE RLC/MAC thatthe UL data that were transmitted are acknowledged and(re-)transmissions should be stopped.

If the UE receives RRC connection release or reject message notindicating ACK to the UL data, the UE may consider that the UL data thatwere transmitted are unacknowledged and enter RRC_IDLE. The UE maytrigger RRC connection establishment procedure or RRC connection resumeprocedure to re-transmit unacknowledged data later.

If the UE transmits data over SRB or DRB, and if the UE receives a RRCconnection setup message (or a RRC connection resume message) indicatingthat the data are acknowledged, the UE may not transmit a RRC connectionsetup complete message (or a RRC connection resume complete message),and consider the RRC procedure successful, and then enter RRC_IDLE.

If the UE transmits data over SRB or DRB, and if the RRC connectionestablishment or the RRC connection resume procedure with EDT fails,e.g. the procedure unsuccessfully ends due to reception of the RRCconnection reject or T300 expiry, the UE may consider that the data areunacknowledged in Layer 1, 2 or 3, and the UE may stop(re-)transmissions of any data and RLC/MAC acknowledgements, if any.Then, if the data has been transmitted over DRB (or SRB), the UE mayre-establish and suspend Layer 2 entities. If the data has beentransmitted over SRB, the UE may release Layer 2 entities. Finally, theUE may enter RRC_IDLE and may trigger the RRC connection establishmentor the RRC connection resume procedure for re-transmission of the datathat was not delivered and unacknowledged in Layer 1, 2 or 3.

According to an embodiment of the present invention, the UE may performinitial transmission over one type of SRB and re-transmission overanother type of SRB, based on a RRC (or NAS) message indicating NACK tothe initial transmission over SRB. If the UE receives RRC connectionsetup message or RRC connection resume message indicating NACK to thedata transmission over SRB, the UE may re-transmit the data in the sametype of message (e.g. RRC connection request message or RRC connectionresume message) or another type of message (e.g. RRC connection setupcomplete message or RRC connection resume complete message). If the UEreceives a CCCH message indicating NACK to the data transmission overSRB, the UE may re-transmit the data over CCCH regardless of setup ofDCCH. If the UE receives a CCCH message indicating NACK to the datatransmission over SRB, the UE may re-transmit the data over DCCH, ifDCCH is set up. The embodiment of the present invention may be appliedtogether with the example in FIGS. 11A and 11B.

FIGS. 11A and 11B show a procedure for performing EDT according to anembodiment of the present invention.

Referring to FIGS. 11A and 11B, in step S1100, the UE may camp on acell. For example, the cell may be a NB-IoT cell or a LTE cellsupporting one or more narrowband for low cost UE capabilities suchCategory M1. System information may broadcast at least one ofconfiguration of CCCH2 for EDT, configuration of radio bearers (e.g.DRBs including DTCHs) mapped to EDT, RAPID indicating EDT or LCID ofCCCH2 for EDT. Each cell may inform one or more UEs that this cellsupports EDT for the Control Plane CIoT EPS optimization and/or EDT forthe User Plane CIoT EPS optimization via system information.

If the cell indicates EDT for the Control Plane CIoT EPS optimization,the UE supporting EDT for Control Plane CIoT EPS optimization mayconfigure CCCH2 for EDT. In this case, the UE may configure twodifferent CCCH logical channels for uplink. The first CCCH logicalchannel may have a higher priority than the second CCCH logical channelin MAC logical channel prioritization. The first CCCH logical channelmay be SRB0 while the second CCCH logical channel may be SRB0bis. Thefirst CCCH logical channel may be applicable for uplink and downlink,while the second CCCH logical channel may be applicable only for uplink.The first CCCH logical channel may have a higher priority than all MACCEs. The second CCCH logical channel may have a lower priority than acertain MAC CE(s) (e.g. The Data Volume and Power Headroom Report (DPR)MAC CE, Buffer Status Report MAC CE, Power Headroom MAC CE), and ahigher priority than the other MAC CE(s). Alternatively, both CCCHlogical channels may have a higher priority than all MAC CEs. The CCCH2may be replaced by DCCH mapped to EDT or a legacy CCCH. For example,DCCH mapped to EDT may be used to carry EDT instead of CCCH2. However,DCCH not mapped to EDT may not be used to carry EDT.

If the cell does not indicate EDT, UE does not perform EDT.

If the UE detects UL data and CCCH2 is configured, the UE may submit theUL data to lower layers over CCCH type 2 (e.g. an RLC entity of CCCH2for SRB0bis). If the UE detects UL data and a DTCH mapped to EDT isconfigured, the UE may submit the UL data to lower layers (RLC/PDCPentities) over the DTCH mapped to EDT.

If the UE detects UL data, the UE may also trigger RRC connectionestablishment procedure or RRC connection resume procedure. The RRCconnection request message or the RRC connection resume request messagemay be submitted to CCCH1 for SRB0.

In step S1110, if a random access procedure is triggered, the MAC layerof the UE (i.e. UE MAC) may select one of random access preambleidentifiers (RAPIDs) mapped to EDT (as received from the cell via systeminformation). Then, the UE may transmit a random access preamble withthe selected random access preamble identifier (RAPID).

In step S1120, the UE MAC may receive a random access response (RAR)message indicating the transmitted RAPID and an uplink grant. If the UEMAC receives no RAR indicating the transmitted RAPID, the UE MACre-transmits a random access preamble with power ramping.

In step S1130, the UE MAC may perform logical channel prioritization.Then, the UE MAC may construct MAC PDU based on logical channelpriorities and the uplink grant. In the logical channel prioritization,CCCH1 and CCCH2 may have a higher priority than all MAC CEs.

In the MAC PDU, if data from CCCH is included, LCID indicating CCCH maybe included as a MAC sub-header. In addition, if data from CCCH2 isincluded, LCID indicating CCCH2 may be included as a MAC sub-header.

If the received UL grant can accommodate all UL data in CCCH2, and ifthe UE has no remaining UL data over any logical channel, the UE mayinclude BSR MAC CE indicating no data, DPR MAC CE indicating no data(i.e. DV value=0), or no MAC CE.

If the received UL grant can accommodate some UL data in CCCH2 with aMAC CE such as BSR MAC CE or DPR MAC CE, and if UE has remaining UL dataover any logical channel, the UE may include BSR MAC CE indicating theamount of the remaining UL data or DPR MAC CE indicating the amount ofthe remaining UL data.

If the received UL grant cannot accommodate any UL data in CCCH2 with aMAC CE such as BSR MAC CE or DPR MAC CE, the UE may include BSR MAC CEindicating the amount of the remaining UL data or DPR MAC CE indicatingthe amount of the remaining UL data.

In step S1140, the UE MAC may transmit the MAC PDU (i.e. Message 3(MSG3)) to the base station by using the uplink grant.

In step S1150, if the UE MAC may receive contention resolution to themessage 3 from the base station (e.g. via PDCCH or Contention ResolutionMAC CE), the UE MAC may consider the RACH procedure successful.Otherwise, the UE MAC may re-transmit a random access preamble.

In step S1160, the UE may receive RRC connection setup message or RRCconnection resume message from the base station. If the received messageindicates NACK to EDT, the layer of the UE received the NACK may sendthe NACK to a higher layer of the UE. For example, for EDT over SRB inControl Plane CIoT EPS optimization, if the UE RRC receives the NACKfrom the message, the UE RRC may inform UE NAS about the NACK to the ULdata. Upon receiving the NACK, the higher layer of the UE (e.g. UE NAS)may re-transmit the UL data. If so, the UE RRC may create a RRC messageincluding the UL data and submit the RRC message to lower layers (i.e.PDCP/RLC/MAC). The RRC message may be carried over either CCCH2 or DCCH.

In step S1170, if the message is carried over DCCH, the message can be aRRC connection setup/resume complete including UL data. The UL data caninclude UL data which is NACKed and/or remaining UL data. Thus, UE maytransmit a single MAC SDU including RRC connection setup/resume completeincluding UL data with a MAC CE in a single MAC PDU.

In step S1175, if the message is carried over CCCH such as CCCH2, the UEmay transmit a RRC connection setup/resume complete message over DCCHand the message including UL data over CCCH with a MAC CE in a singleMAC PDU or separate MAC PDUs. The UL data can include UL data which isNACKed and/or remaining UL data.

The MAC CE in the MAC PDU can be either BSR MAC CE indicating the amountof the remaining UL data or DPR MAC CE indicating the amount of theremaining UL data. If there is no remaining UL data except the UL dataincluded in the MAC PDU, the MAC CE may indicate no data.

In step S1180, if the MAC CE indicates no data, and if the base stationsuccessfully receives all UL data, in case there is no DL data, the basestation may transmit RRC Connection release indicating ACK to the ULdata. Upon receiving the RRC connection release indicating ACK to the ULdata, the UE may consider that the UL data that were transmitted areacknowledged and enter RRC_IDLE. The UE RRC may inform UE RLC/MAC thatthe UL data that were transmitted are acknowledged and(re-)transmissions should be stopped.

If the UE receives RRC connection release not indicating ACK to the ULdata, the UE may consider that the UL data that were transmitted areunacknowledged and enter RRC_IDLE. The UE may trigger RRC connectionestablishment procedure or RRC connection resume procedure tore-transmit unacknowledged data later.

FIG. 12 is a block diagram illustrating a method for a UE to perform EDTaccording to an embodiment of the present invention.

Referring to FIG. 12, in step S1210, the UE may receive systeminformation including a threshold for the EDT. The UE may be in aRRC_IDLE. The UE may be an NB-IoT UE. The threshold for the EDT may be athreshold related to the size of data for the EDT.

In step S1220, the UE may determine whether or not a condition (e.g.first condition) for initiating the EDT is satisfied, by comparing thethreshold for the EDT with a size of data for transmission. The EDT maybe an uplink data transmission during a random access procedure.

The UE may determine that the condition for initiating the EDT issatisfied, if the size of data for transmission is lower than thethreshold for the EDT. The UE may determine that the condition forinitiating the EDT is not satisfied, if the size of data fortransmission is higher than the threshold for the EDT. The size of datamay be a data size in a layer 2 including MAC layer. The size of datafor transmission may be uplink data available for transmission plus MACheader.

The threshold for the EDT may be a threshold related to delayrequirement for the EDT. In this case, the UE may further determinewhether or not a condition (e.g. second condition) for initiating theEDT is satisfied, by comparing the threshold for the EDT with the delayrequirement of the data. The UE may determine that the condition forinitiating the EDT is satisfied, if the delay requirement of the data islower than the threshold for the EDT. The UE may determine that thecondition for initiating the EDT is not satisfied, if the delayrequirement of the data is higher than the threshold for the EDT.

In step S1230, the UE may perform the EDT if the condition is satisfied.

In step S1240, the UE may perform a RRC connection establishment orresume procedure if the condition is not satisfied. Furthermore, the UEmay perform data transmission after the RRC connection establishment orresume procedure is performed, if the condition is not satisfied.

According to an embodiment of the present invention, the UE candetermine whether or not to perform EDT during the random accessprocedure. For example, in case that the size of data for transmissionis lower than the threshold for EDT, the UE may transmit data to thebase station by using message 3 during the random access procedure. Forexample, in case that the size of data for transmission is lower thanthe threshold for EDT and the delay requirement of the data is lowerthan the threshold for the EDT, the UE may transmit data to the basestation by using message 3 during the random access procedure. Thus, thepower consumption of the UE (e.g. low cost UE) can be reduced.

FIG. 13 is a block diagram illustrating a wireless communication systemaccording to the embodiment of the present invention.

A BS 1300 includes a processor 1301, a memory 1302 and a transceiver1303. The memory 1302 is connected to the processor 1301, and storesvarious information for driving the processor 1301. The transceiver 1303is connected to the processor 1301, and transmits and/or receives radiosignals. The processor 1301 implements proposed functions, processesand/or methods. In the above embodiment, an operation of the basestation may be implemented by the processor 1301.

A UE 1310 includes a processor 1311, a memory 1312 and a transceiver1313. The memory 1312 is connected to the processor 1311, and storesvarious information for driving the processor 1311. The transceiver 1313is connected to the processor 1311, and transmits and/or receives radiosignals. The processor 1311 implements proposed functions, processesand/or methods. In the above embodiment, an operation of the userequipment may be implemented by the processor 1311.

The processor may include an application-specific integrated circuit(ASIC), a separate chipset, a logic circuit, and/or a data processingunit. The memory may include a read-only memory (ROM), a random accessmemory (RAM), a flash memory, a memory card, a storage medium, and/orother equivalent storage devices. The transceiver may include abase-band circuit for processing a wireless signal. When the embodimentis implemented in software, the aforementioned methods can beimplemented with a module (i.e., process, function, etc.) for performingthe aforementioned functions. The module may be stored in the memory andmay be performed by the processor. The memory may be located inside oroutside the processor, and may be coupled to the processor by usingvarious well-known means.

Various methods based on the present specification have been describedby referring to drawings and reference numerals given in the drawings onthe basis of the aforementioned examples. Although each method describesmultiple steps or blocks in a specific order for convenience ofexplanation, the invention disclosed in the claims is not limited to theorder of the steps or blocks, and each step or block can be implementedin a different order, or can be performed simultaneously with othersteps or blocks. In addition, those ordinarily skilled in the art canknow that the invention is not limited to each of the steps or blocks,and at least one different step can be added or deleted withoutdeparting from the scope and spirit of the invention.

The aforementioned embodiment includes various examples. It should benoted that those ordinarily skilled in the art know that all possiblecombinations of examples cannot be explained, and also know that variouscombinations can be derived from the technique of the presentspecification. Therefore, the protection scope of the invention shouldbe determined by combining various examples described in the detailedexplanation, without departing from the scope of the following claims.

What is claimed is:
 1. A method for transmitting, by a user equipment(UE), in a radio resource control (RRC) idle state, uplink data during arandom access procedure in a wireless communication, the methodcomprising: receiving system information including (i) a threshold forearly data transmission (EDT) and (ii) information representing that theEDT is allowed, from a base station (BS); determining that a conditionfor initiating the EDT is satisfied, based on the informationrepresenting that the EDT is allowed, by comparing the threshold for theEDT with a size of the uplink data for transmission; transmitting arandom access preamble which is configured for the EDT, to the BS;receiving a random access response message from the BS; in response tothe random access response message, transmitting a first RRC messageincluding the uplink data to the BS during the random access procedure;and in response to the first RRC message, receiving a second RRC messagerelated to a success of the EDT, from the BS, wherein the RRC idle stateis maintained by the UE based on the second RRC message related to thesuccess of the EDT.
 2. The method of claim 1, wherein the size of theuplink data for transmission is lower than the threshold for the EDT. 3.The method of claim 1, wherein the threshold for the EDT is a thresholdrelated to the size of the uplink data for the EDT.
 4. The method ofclaim 1, wherein the size of the uplink data is a data size in a layer 2including a medium access control (MAC) layer.
 5. The method of claim 1,wherein the threshold for the EDT is a threshold related to delayrequirement for the EDT.
 6. The method of claim 5, further comprising:determining whether or not a condition for initiating the EDT issatisfied, by comparing the threshold for the EDT with the delayrequirement of the uplink data.
 7. The method of claim 6, wherein the UEdetermines that the condition for initiating the EDT is satisfied, whenthe delay requirement of the uplink data is lower than the threshold forthe EDT.
 8. The method of claim 6, wherein the UE determines that thecondition for initiating the EDT is not satisfied, when the delayrequirement of the uplink data is higher than the threshold for the EDT.9. The method of claim 1, wherein the size of the uplink data fortransmission is uplink data available for transmission plus MAC header.10. The method of claim 1, wherein the UE is a Narrow Band Internet ofThings (NB-IoT) UE.
 11. The method of claim 1, wherein the UEcommunicates with at least one of a mobile terminal, a network orautonomous vehicles other than the UE.
 12. A user equipment (UE)transmitting uplink data during a random access procedure in a wirelesscommunication, the UE comprising: at least one transceiver; at least oneprocessor; and at least one computer memory operably connectable to theat least one processor and storing instructions that, when executed,cause the at least one processor to perform operations comprising:receiving system information including (i) a threshold for early datatransmission (EDT) and (ii) information representing that the EDT isallowed, from a base station (BS); determining that a condition forinitiating the EDT is satisfied, based on the information representingthat the EDT is allowed, by comparing the threshold for the EDT with asize of the uplink data for transmission; transmitting a random accesspreamble which is configured for the EDT, to the BS; receiving a randomaccess response message from the BS; in response to the random accessresponse message, transmitting a first RRC message including the uplinkdata to the BS during the random access procedure; and in response tothe first RRC message, receiving a second RRC message related to asuccess of the EDT, from the BS, wherein the RRC idle state ismaintained by the UE based on the second RRC message related to thesuccess of the EDT.